1. Field of the Invention
The present invention relates to an exhaust gas cleaning system for an internal combustion engine, such as a diesel engine, that uses a particulate filter to collect and remove particulate matter in an exhaust gas discharged from the engine. More specifically, the present invention relates to a method of determining a particulate matter accumulation state of the particulate filter.
2. Background Information
Harmful exhaust components such as carbon particles and other particulate matters (particulate matter or “PM”) contained in an exhaust gas have become an enormous problem especially in diesel engines. Conventionally, various types of particulate matter capturing filters (Diesel Particulate Filter or “DPF”) have been used as exhaust gas after-treatment devices to collect and remove the particulate matter contained in the exhaust gas.
When this type of particulate filter is used, the particulate filter needs to be regenerated when an amount of accumulated particulate matter reaches a prescribed amount by combusting the particulate matter accumulated in the particulate filter. Therefore, it is necessary to determine or estimate an amount or degree of the particulate matter accumulated in the particulate filter.
Some of the conventional methods are configured to estimate the amount of particulate matter accumulated in the particulate filter by utilizing a phenomenon that the pressure loss of the particulate filter increases as an amount of particulate matter accumulated in the particulate filter increases.
For example, Japanese Laid-Open Patent Publication No. 6-341312 describes a technology in which pressure sensors are arranged on the upstream side and downstream side of a particulate filter installed in an exhaust passage of the engine. The sensors are arranged to detect the pressure difference between before and after the particulate filter, i.e., the pressure loss resulting from the exhaust gas passing through the particulate filter. Additionally, in the above mentioned reference, the detected pressure difference is corrected based on the exhaust gas temperature and the engine rotational speed to obtain a corrected pressure loss. The corrected pressure loss is used to determine a particulate matter accumulation amount in the particulate filter.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved exhaust gas cleaning system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.